Dissolve tea in hot water in a small cup. Transfer to refrigerator for 15 minutes to cool. Pour sea salt onto a small plate. Rub a wedge of lime onto one side of a cocktail glass and dip into sea salt. Add 1 cup of ice to a cocktail glass. Set aside.
Add 1/2 cup of ice to a pint glass. Pour in chilled tea, tequila, lime juice, grapefruit juice, and agave nectar. Stir for 5 seconds to combine. Strain into cocktail glass over fresh ice. Garnish with a slice of grapefruit.